A reaction for the N-alkylation of amines is an industrially important reaction. As this reaction, techniques using methyl iodide, dimethyl sulfate and the like as alkylating agents are known, but many of the alkylating agents are mutagenic substances, and thus safer techniques are desired. One of the safer techniques includes alkylation using a transition metal as a catalyst wherein an alcohol is used as a carbon source.
Examples of the catalyst include heterogeneous catalysts and homogeneous catalysts comprising platinum or chromium. Since heterogeneous catalysts generally require a high temperature and a high pressure and thus have problems in safeness, homogeneous catalysts are more advantageous in industry.
As homogeneous catalysts, complexes comprising metals such as iridium, rhodium and ruthenium are known.
As examples using an iridium complex, monoalkylation of an amine using an alcohol catalyzed by an arene-type complex described in Non Patent Documents 1 and 2, and alkylation of a heteroamine with a complex bearing a P,N ligand described in Non Patent Document 3 are known. Furthermore, as an example using methanol as a carbon source, the example described in Non Patent Document 4 is known.
Regarding ruthenium, the reaction for dimethylating an amine using methanol as a carbon source described in Non Patent Document 5 is known. Furthermore, Non Patent Document 6 describes a reaction for monomethylating an aniline using methanol as a carbon source and using ruthenium trichloride and a trialkoxyphosphine as catalysts.
Ruthenium is more advantageous in industry than iridium and rhodium since it is an inexpensive metal. Ruthenium complexes that catalyze an N-methylation reaction using an alcohol are reported in Non Patent Documents 5, 6, 7 and the like, but any example of a report in which a Pincer type ruthenium complex having a tridentate ligand is used is not known. Furthermore, reactions using the ruthenium complexes described in said Non Patent Documents require a much amount of catalyst, there are problems in costs and the like for industrialization.
Furthermore, as a catalyst for reducing a carbonyl group in a ketone, an ester or the like, a ruthenium complex having a tridentate ligand and a carbonyl ligand, wherein the tridentate ligand comprises two phosphino groups and a —NH— group, has been already reported (see Patent Document 1). However, said documents are silent about a catalytic ability in alkylation of an amines.